Motor drive control device

Abstract

To measure a current of a coil of a motor with high accuracy.SOLUTION: A motor driving control device 10 comprises: a control circuit 1 that generates a driving control signal Sd on the basis of a measurement value of a current i flowing through a coil 31 of a motor 3; and a driving circuit 2 that drives the coil 31 based on the driving control signal Sd. The driving circuit 2 comprises: a switch SW1 and a switch SW2 that are connected in series; a switch SW3 and a switch SW4 that are connected in series; a current detection element R1 that is connected in series to the switch SW1 and the switch SW2; and a current detection element R2 that is connected in series to the switch SW3 and the switch SW4. The coil 31 is connected between a node A+ to which the switch SW1 and the switch SW2 are commonly connected and an anode A- to which the switch SW3 and the switch SW4 are commonly connected. The control circuit 1 measures the current i on the basis of a mean value of a current i1 flowing through the current detection element R1 and a current i2 flowing through the current detection element R2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a motor drive control device. [Background technology]

[0002] Generally, a motor drive control device for driving a motor such as a hybrid stepping motor using PWM (Pulse Width Modulation) measures the current flowing through the motor's coil and adjusts the duty ratio of the PWM signal, which serves as a drive control signal for the motor, based on the measured current value, thereby controlling the motor to operate with an appropriate torque.

[0003] As a method for measuring the current flowing through the coil of a motor, for example, as disclosed in Patent Document 1, a technique is known in which a current detection resistor is connected to the low side of an inverter circuit (H-bridge circuit) that drives the motor, and the current flowing through the current detection resistor is measured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-182942 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional current measurement methods, such as those described in Patent Document 1, detect current using a single resistor connected in series to an inverter circuit, which serves as a motor drive circuit. As a result, the coil current cannot be detected properly due to switching noise, etc., generated when the switch constituting the inverter circuit is driven, which may result in reduced detection accuracy.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to make it possible to measure the current in the coil of a motor with high accuracy. [Means for solving the problem]

[0007] A motor drive control device according to a representative embodiment of the present invention comprises a control circuit that generates a drive control signal for driving a coil of a motor based on a measurement of a current flowing through the coil, and a drive circuit that drives the coil based on the drive control signal generated by the control circuit, wherein the drive circuit includes a first switch and a second switch connected in series, a third switch and a fourth switch connected in series, a first current detection element connected in series with the first switch and the second switch, and a second current detection element connected in series with the third switch and the fourth switch, the coil is connected between a first node to which the first switch and the second switch are commonly connected and a second node to which the third switch and the fourth switch are commonly connected, and the control circuit measures the current flowing through the coil based on the average value of the current flowing through the first current detection element and the current flowing through the second current detection element. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to measure the current in the coil of a motor with high accuracy. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing the configuration of a motor unit equipped with a motor drive control device according to a first embodiment. [Figure 2] 2 is a diagram showing the internal configuration of a drive circuit and a control circuit in the motor drive control device according to the first embodiment. FIG. [Figure 3] 3 is a diagram illustrating an example of an internal configuration of a current obtaining unit according to the first embodiment. FIG. [Figure 4] 4 is a diagram for explaining the timing of measuring the current of the coil by the current acquiring unit according to the first embodiment. FIG. [Figure 5A] FIG. 4 is a diagram showing an example of a current flow pattern of a coil. [Figure 5B]FIG. 4 is a diagram showing an example of a current flow pattern of a coil. [Figure 6] FIG. 10 is a diagram showing the internal configuration of a drive circuit and a control circuit in a motor drive control device according to a second embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of an internal configuration of a current obtaining unit according to a second embodiment. [Figure 8] 10 is a diagram for explaining the timing of measuring the current of the coil by the current acquiring unit according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings. In the following description, components common to the embodiments will be designated by the same reference numerals, and repeated description will be omitted.

[0011] First Embodiment FIG. 1 is a diagram showing the configuration of a motor unit 100 equipped with a motor drive control device 10 according to the first embodiment.

[0012] 1, the motor unit 100 includes a motor 3, a rotational position detector 4 for detecting the rotational position of the motor 3, and a motor drive control device 10 for controlling the rotation of the motor 3. The motor unit 100 can be applied to various devices, such as fans, that use a motor as a drive source.

[0013] The motor 3 is, for example, a stepping motor having two-phase (A-phase and B-phase) coils.

[0014] The rotational position detector 4 is a device for detecting the rotational position of the rotor of the motor 3. The rotational position detector 4 is, for example, an encoder. The rotational position detector 4 outputs a rotational position detection signal Se corresponding to the rotational position of the rotor of the motor 3. Note that the rotational position detector 4 is not limited to an encoder, and may be a Hall element or the like.

[0015] The motor drive control device 10, for example, periodically passes a drive current through the coils of each phase of the motor 3 to rotate the rotor (permanent magnet) of the motor 3. Specifically, the motor drive control device 10 has a control circuit 1 and a drive circuit 2.

[0016] Note that the components of the motor drive control device 10 shown in FIG. 1 are only a part of the whole, and the motor drive control device 10 may have other components in addition to those shown in FIG.

[0017] FIG. 2 is a diagram showing the internal configuration of the drive circuit 2 and the control circuit 1 in the motor drive control device 10 according to the first embodiment.

[0018] The drive circuit 2 is disposed between a DC power supply VDD and a ground potential GND, and drives a coil 31 of a motor 3 serving as a load based on an input drive control signal Sd.

[0019] Note that Figure 2 only shows the drive circuit 2 for driving the A-phase coil 31 of the A-phase and B-phase coils 31 in the motor 3, and omits the drive circuit 2 and functional blocks for driving the B-phase coil 31.

[0020] 2, the drive circuit 2 is an inverter circuit, for example, an H-bridge circuit. Specifically, the H-bridge circuit serving as the drive circuit 2 includes two switching legs 21 and 22 and two current detection elements R1 and R2 connected in series to the switching legs 21 and 22, respectively.

[0021] More specifically, the drive circuit 2 includes switches SW1 and SW2 connected in series, switches SW3 and SW4 connected in series, current detection elements R1 and R2. The switches SW1 and SW2 form one switching leg 21. The switches SW3 and SW4 form the other switching leg 22. The current detection element R1 is connected in series with the switches SW1 and SW2. The current detection element R2 is connected in series with the switches SW3 and SW4.

[0022] The switches SW1 to SW4 are, for example, transistors. Although the type of transistor is not particularly limited, the switches SW1 to SW4 are, for example, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors).

[0023] The coil 31 of each phase of the motor 3 is connected between the neutral points of the switching legs 21 and 22 of the drive circuit 2. Specifically, as shown in Fig. 2, the coil 31 of the motor 3 is connected between a node A+ to which the switches SW1 and SW2 are commonly connected and a node A- to which the switches SW3 and SW4 are commonly connected. Here, "node A+" refers to the node connected to the terminal of coil 31 on the upstream side of the current when current flows through the A-phase coil 31. On the other hand, "node A-" refers to the node connected to the terminal of coil 31 on the downstream side of the current when current flows through the A-phase coil 31.

[0024] The drive circuit 2 drives a coil 31 as a load by alternately turning on and off (switching operation) two switches SW1 and SW2 (SW3 and SW4) connected in series in response to the input drive control signal Sd.

[0025] When the switches SW1 and SW2 connected in series are switched on and off, a dead time may be provided during which both switches SW1 and SW2 are turned off. A similar dead time may be provided for the switches SW3 and SW4.

[0026] The drive control signal Sd is a signal for controlling the drive of the motor 3. For example, the drive control signal Sd is a PWM (Pulse Width Modulation) signal, and includes four types of signals for individually driving the switches SW1 to SW4. The drive control signal Sd switches the on / off states of the switches SW1 to SW4, thereby switching the current conduction pattern of the coil 31.

[0027] The current detection elements R1 and R2 are elements, such as resistors, for detecting the current flowing through the coil 31 of the motor 3. The current detection element R1 is connected in series with the switches SW1 and SW2 between the DC power supply VDD and ground potential GND. The current detection element R2 is connected in series with the switches SW3 and SW4 between the DC power supply VDD and ground potential GND. For example, the current detection element R1 is connected between the switch SW2 on the low side of the switching leg 21 and ground potential GND. The current detection element R2 is connected between the switch SW4 on the low side of the switching leg 22 and ground potential GND. The currents i1 and i2 flowing through the current detection elements R1 and R2 are converted into voltages by the current detection elements R1 and R2 and input to the control circuit 1 as a current detection signal Si.

[0028] The control circuit 1 generates a drive control signal Sd based on a measured value of the current i flowing through the coil 31 of the motor 3, and controls the driving of the motor 3. Specifically, the control circuit 1 generates the drive control signal Sd based on, for example, a drive command signal Sc indicating a target state of operation of the motor 3, a current detection signal Si, and a rotational position detection signal Se from the rotational position detector 4, so that the motor 3 is in the operating state specified by the drive command signal Sc. The drive command signal Sc is input from an external device. The control circuit 1 also monitors the rotational state of the motor 3 by obtaining information such as the rotational speed and torque of the rotor of the motor 3 based on the current detection signal Si and the rotational position detection signal Se.

[0029] As will be described in detail later, the control circuit 1 measures the current i flowing through the coil 31 of the motor 3 based on the average value of the current i1 flowing through the current detection element R1 and the current i2 flowing through the current detection element R2.

[0030] The control circuit 1 is a program processing device (e.g., a microcontroller) having a configuration in which a processor such as a CPU, various storage devices such as RAM and ROM, and peripheral circuits such as a counter (timer), an A / D conversion circuit, a D / A conversion circuit, a clock generation circuit, and an input / output I / F circuit are connected to each other via a bus or dedicated lines.

[0031] The motor drive control device 10 may be configured such that at least a portion of the control circuit 1 and at least a portion of the drive circuit 2 are packaged as a single integrated circuit device (IC), or such that the control circuit 1 and the drive circuit 2 are each packaged as separate integrated circuit devices.

[0032] The specific configuration and operation of the control circuit 1 will be described in detail below.

[0033] As shown in FIG. 2, the control circuit 1 has, for example, a drive control unit 11, a current acquisition unit 12, a rotational speed acquisition unit 13, and a position acquisition unit 14 as functional blocks for generating the drive control signal Sd.

[0034] These functional blocks are realized, for example, by a processor in a program processing device serving as the control circuit 1, which executes various arithmetic operations according to programs stored in memory and controls peripheral circuits such as counters and A / D conversion circuits.

[0035] The rotational speed acquisition unit 13 is a functional unit that acquires a measured value of the rotational speed of the rotor of the motor 3. The rotational speed acquisition unit 13 calculates the rotational speed ω of the rotor of the motor 3 based on, for example, the rotational position detection signal Se output from the rotational position detector 4.

[0036] The position acquisition unit 14 is a functional unit that acquires a measurement value of the rotation angle of the rotor of the motor 3. The position acquisition unit 14 calculates the rotation angle (rotation position) θ of the rotor of the motor 3 based on, for example, the rotation position detection signal Se output from the rotation position detector 4.

[0037] The current acquisition unit 12 is a functional unit that acquires a measured value of the current of the coil 31 of the motor 3 . Based on the current detection signal Si, the current obtaining unit 12 calculates a measurement value of the current i flowing through the corresponding phase coil 31. The method of measuring the current i by the current obtaining unit 12 will be described later.

[0038] The control circuit 1 has a current acquisition unit 12 for each coil 31 (drive circuit 2) of each phase of the motor 3, but Figure 2 only shows the current acquisition unit 12 that detects the current flowing through the coil 31 of phase A.

[0039] The drive control unit 11 calculates the control amount of the motor 3, for example, by performing a calculation based on vector control, based on the drive command signal Sc, the current i of the coil 31 acquired by the current acquisition unit 12, the rotational speed ω of the motor 3 acquired by the rotational speed acquisition unit 13, and the rotational angle θ of the motor 3 acquired by the position acquisition unit 14, and generates a drive control signal Sd based on the calculated control amount.

[0040] For example, the drive control unit 11 includes a drive command acquisition unit 15, a position control unit 16, a speed control unit 17, a current control unit 18, and a drive control signal generation unit 19.

[0041] The drive command acquisition unit 15 receives the drive command signal Sc and analyzes the received drive command signal Sc to acquire a value specifying a target operating state of the motor 3 specified by the drive command signal Sc. For example, the drive command signal Sc is output from a higher-level device that is provided outside the motor drive control device 10 and that controls the motor unit 100.

[0042] The drive command signal Sc includes a value indicating a target state of operation of the motor 3. In this embodiment, the drive command signal Sc is, for example, a rotation angle command signal that specifies the rotation angle (rotation position) of the motor 3, and includes a target value (target rotation angle) θref of the rotation angle of the rotor of the motor 3. The drive command acquisition unit 15 analyzes the drive command signal Sc to acquire the value of the target rotation angle θref.

[0043] The position control unit 16 calculates a control amount based on the target rotation angle θref acquired by the drive command acquisition unit 15. Specifically, the position control unit 16 calculates a control amount according to (θref-θ) between the target rotation angle θref and the rotation angle θ acquired by the position acquisition unit 14. For example, the position control unit 16 calculates a control amount of the motor 3 by PI control calculation so that the error (θref-θ) becomes zero, converts the control amount into a rotation speed value, and outputs it as the target rotation speed ωref.

[0044] The speed control unit 17 calculates a control amount based on the target rotational speed ωref calculated by the position control unit 16. Specifically, the speed control unit 17 calculates a control amount according to the difference (ωref-ω) between the target rotational speed ωref and the rotational speed ω acquired by the rotational speed acquisition unit 13. For example, the speed control unit 17 calculates a control amount of the motor 3 by PI control calculation so that the error (ωref-ω) becomes zero, converts the control amount into a current (coil current) value, and outputs it as the target current iref.

[0045] The current control unit 18 calculates a control amount based on the target current iref calculated by the speed control unit 17. Specifically, the current control unit 18 calculates a control amount according to the difference (iref-i) between the target current iref and the current i acquired by the current acquisition unit 12. For example, the current control unit 18 calculates the control amount of the motor 3 by PI control calculation so that the error (iref-i) becomes zero, and outputs the control amount as a voltage command value vref.

[0046] The drive control signal generation unit 19 generates the drive control signal Sd based on the voltage command value vref calculated by the current control unit 18. For example, the drive control signal generation unit 19 performs space vector transformation based on the voltage command value vref output from the current control unit 18 and the rotation angle θ to generate a voltage signal (PWM signal) in a two-phase (A-phase, B-phase) fixed coordinate system and outputs it as the drive control signal Sd.

[0047] Here, a method for measuring the current i flowing through the coil 31 of the motor 3 by the current acquisition unit 12 of the control circuit 1 will be described. Although a method for measuring the current flowing through the A-phase coil 31 of a two-phase stepping motor will be described below, the current flowing through the B-phase coil is also measured in the same manner as for the A-phase coil.

[0048] FIG. 3 is a diagram illustrating an example of the internal configuration of the current obtaining unit 12 according to the first embodiment.

[0049] The current acquiring unit 12 acquires a measured value of the current i flowing through the coil 31 based on the average value of the current i1 flowing through the current detecting element R1 and the current i2 flowing through the current detecting element R2 in the drive circuit 2.

[0050] 3, the current acquiring unit 12 has a first current detecting unit 121, a second current detecting unit 122, and a current value calculating unit 123. The first current detecting unit 121 detects the value of a current i1 flowing through a current detecting element R1. The second current detecting unit 122 detects the value of a current i2 flowing through a current detecting element R2. The current value calculating unit 123 calculates an average value (e.g., an arithmetic average value) of the value of the current i1 detected by the first current detecting unit 121 and the value of the current i2 detected by the second current detecting unit 122, and outputs the average value as a measurement value of the current i of the coil 31.

[0051] FIG. 4 is a diagram for explaining the timing of measuring the current of the coil 31 by the current acquiring unit 12 according to the first embodiment. 5A and 5B are diagrams showing an example of a current flow pattern for the coil 31. FIG.

[0052] FIG. 4 shows, for example, the on / off states of the switches SW1 to SW4 when the duty ratio of the drive control signal Sd on the node A+ side (SW1, SW2) and the node A- side (SW3, SW4) is 50%, respectively, and the voltages across the coil 31, i.e., the voltages at the nodes A+ and A-.

[0053] As shown in FIG. 4, the duty ratio (pulse width) of the drive control signal Sd changes from the midpoint of the PWM period to both ends of the PWM period.

[0054] Fig. 5A shows the on / off states of the switches SW1 to SW4 and the current paths when exciting the coil 31 (excitation mode). Fig. 5B shows the on / off states of the switches SW1 to SW4 and the current paths when regenerating the current in the coil 31 (regeneration mode).

[0055] The drive control signal Sd alternately turns on the switches SW1 and SW2, and alternately turns on the switches SW3 and SW4. For example, when switches SW1 and SW4 are turned on and switches SW2 and SW3 are turned off, coil 31 enters the excitation mode, and as shown in FIG. 5A, current i flows from DC power supply VDD through switch SW1, coil 31, and switch SW4 to ground potential GND.

[0056] Furthermore, after the above excitation mode, when the switches SW1 and SW3 are turned off and the switches SW2 and SW4 are turned on, the coil 31 enters the regeneration mode, and as shown in FIG. 5B, a current i is regenerated from the ground potential GND through the switch SW2, the coil 31, and the switch SW4 to the ground potential GND.

[0057] The switches SW1 to SW4 perform switching operations in accordance with the drive control signal Sd, thereby switching the direction of the current i flowing through the coil 31 and repeatedly switching between the excitation mode and the regeneration mode.

[0058] For example, as shown in Fig. 4, the current i flowing through the coil 31 when the duty of the PWM period is 50% will be described. When the duty of the PWM period is 50%, the current value of the current i flowing through the coil 31 is maintained.

[0059] When the duty cycle of the PWM period is 50%, the period during which switches SW1 and SW3 are off and switches SW2 and SW4 are on lasts for 25% of the PWM period. At this time, current i is regenerated from ground potential GND to ground potential GND through switch SW2, coil 31, and switch SW4. Next, the period during which switches SW1 and SW3 are on and switches SW2 and SW4 are off lasts for 50% of the PWM period. At this time, current i is regenerated from DC power supply VDD to DC power supply VDD through switch SW3, coil 31, and switch SW1. Finally, the period during which switches SW1 and SW3 are off and switches SW2 and SW4 are on lasts for 25% of the PWM period. At this time, current i is regenerated from ground potential GND to ground potential GND through switch SW2, coil 31, and switch SW4.

[0060] In this way, when the duty of the PWM period is 50%, the current i flowing through the coil 31 is equal for each direction of the current i, so there is no increase or decrease in the amount of current.

[0061] The current acquisition unit 12 detects a current i1 flowing through the current detection element R1 and a current i2 flowing through the current detection element R2 at a predetermined timing in one cycle (PWM cycle) of the PWM signal serving as the drive control signal Sd. For example, as shown in Fig. 4, at a predetermined timing ts in the PWM cycle of the drive control signal Sd, the first current detection unit 121 samples the value of the current i1 flowing through the current detection element R1, and the second current detection unit 122 samples the value of the current i2 flowing through the current detection element R2.

[0062] In this way, the current value calculation unit 123 calculates the average value of the currents i1 and i2 sampled by the first current detection unit 121 and the second current detection unit 122. As a result, the measured value of the current i flowing through the coil 31 is updated for each PWM period of the drive control signal Sd.

[0063] The timing for detecting (sampling) the currents i1 and i2 is not particularly limited, but is preferably, for example, a period during which the motor 3 is in a regenerative mode, as shown in FIG.

[0064] The period during which the motor 3 is in the regenerative mode may not only be the period during which the switches SW1 and SW3 are off and the switches SW2 and SW4 are on, but also the period during which the current i is regenerated to the ground potential GND via the parasitic diodes of the low-side switches SW2 and SW4.

[0065] As described above, when controlling the drive of the motor 3, the motor drive control device 10 according to the first embodiment measures the currents i1 and i2 flowing through the two current detection elements R1 and R2 connected in series to the two switching legs 21 and 22 that constitute the H-bridge circuit as the drive circuit 2, and determines the average value of the current i1 and the current i2 as the measured value of the current i flowing through the coil 31.

[0066] This makes it possible to properly measure the magnitude of the current flowing through the coil by calculating the average value of the current flowing through the two resistors, even if the current flowing through the coil is unstable due to switching noise or the like when driving the switch elements that make up the inverter circuit.

[0067] Therefore, motor drive control device 10 according to this embodiment makes it possible to measure the coil current with higher accuracy than the conventional method of detecting the coil current of a motor using a single resistor.

[0068] Second Embodiment FIG. 6 is a diagram showing the internal configuration of a drive circuit 2 and a control circuit 1A in a motor drive control device 10A according to the second embodiment.

[0069] The control circuit 1A of embodiment 2 differs from the control circuit 1 of embodiment 1 in that it measures the current i flowing through the coil 31 of the motor 3 by detecting at least one of the currents i1, i2 flowing through the current detection elements R1, R2 in accordance with the duty ratio of the drive control signal Sd, which is a PWM signal, but is otherwise similar to the control circuit 1 of embodiment 1.

[0070] Specifically, when the duty ratio of the drive control signal Sd (PWM signal) is smaller than a predetermined threshold, the control circuit 1A detects the current i1 flowing through the current detection element R1 and the current i2 flowing through the current detection element R2, and calculates the measured value of the current i flowing through the coil 31 based on the average value of the current i1 and the current i2. On the other hand, when the duty ratio of the drive control signal Sd is equal to or greater than a predetermined threshold, the control circuit 1A detects the current flowing through the current detection element R1 or R2 that is downstream in the current path in the drive circuit 2, and calculates the measured value of the current i flowing through the coil 31 based on the detected current.

[0071] FIG. 7 is a diagram illustrating an example of the internal configuration of the current obtaining unit 12A according to the second embodiment. As shown in FIG. 7, the current obtaining section 12A has a first current detecting section 121, a second current detecting section 122, a duty ratio determining section 124, and a current value calculating section 123A.

[0072] As in the first embodiment, the first current detection unit 121 and the second current detection unit 122 sample the currents i1 and i2, respectively, at predetermined timings in the PWM period.

[0073] The duty ratio determination unit 124 measures the duty ratio of the drive control signal Sd, determines whether the duty ratio of the drive control signal Sd is equal to or greater than a predetermined threshold, and outputs the determination result. Although not particularly limited, the predetermined threshold is, for example, a duty ratio of 80%.

[0074] The current value calculation unit 123A calculates the measurement value of the current i flowing through the coil 31 based on the determination result of the duty ratio determination unit .

[0075] Specifically, when the duty ratio determination unit 124 determines that the duty ratio of the drive control signal Sd is smaller than a predetermined threshold, the current value calculation unit 123A calculates the average value of the current i1 flowing through the current detection element R1 and the current i2 flowing through the current detection element R2, and outputs this average value as the measurement value of the current i flowing through the coil 31.

[0076] On the other hand, when the duty ratio determination unit 124 determines that the duty ratio of the drive control signal Sd is equal to or greater than a predetermined threshold, the current value calculation unit 123A outputs, as a measurement value of the current i, the current flowing through one of the current detection elements R1 and R2, which is the current detection element downstream of the current path in the drive circuit 2. The downstream current detection element refers to the current detection element provided on the current path from the coil 31 to the ground potential GND when, in the regeneration mode, the current i flows through the coil 31 and is then regenerated to the ground potential GND.

[0077] 5B, when a current i is regenerated from the ground potential GND via the current detection element R1, the switch SW2, the coil 31, the switch SW4, and the resistor R2 to the ground potential GND, the current detection element R2 is downstream of the current detection elements R1 and R2. In this case, the current value calculation unit 123A obtains the current i2 of the current detection element R2 sampled by the second current detection unit 122 and outputs it as the measurement value of the current i.

[0078] 5B, that is, when the current i is regenerated from the ground potential GND via the current detection element R2, the switch SW4, the coil 31, the switch SW2, and the resistor R1 to the ground potential GND, the current detection element R1 of the current detection elements R1 and R2 is downstream in the current path. In this case, the current value calculation unit 123A acquires the current i1 of the current detection element R1 sampled by the first current detection unit 121 and outputs it as the measurement value of the current i.

[0079] FIG. 8 is a diagram for explaining the timing of measuring the current of the coil 31 by the current acquiring unit 12A according to the second embodiment.

[0080] Figure 8 shows a case where, in a given PWM period T1, the duty ratio of the drive control signal Sd on the node A+ side (SW1, SW2) and the node A- side (SW3, SW4) is 50%, and in the next PWM period T2, the duty ratio of the drive control signal Sd on the node A+ side (SW1, SW2) is 90%, and the duty ratio of the drive control signal Sd on the node A- side (SW3, SW4) is 10%.

[0081] As in the first embodiment, the duty ratio (pulse width) of the drive control signal Sd varies from the midpoint of the PWM period to both ends of the PWM period.

[0082] For example, as shown in FIG. 8, the node A+ side (SW1, SW2) and the node A- side (SW3, SW 4) In the PWM period T1 where the duty ratio of the drive control signal Sd is 50%, there is a sufficient time difference between the timing ts at which the currents i1 and i2 are detected and the timing tx at which the switches SW1 to SW4 switch between on and off, so the current i flowing through the coil 31 is less susceptible to the switching noise of the switches SW1 to SW4.

[0083] On the other hand, as shown in Figure 8, in a PWM period T2 in which the duty ratio of the drive control signal Sd on the node A+ side (SW1, SW2) is 90% and the duty ratio of the drive control signal Sd on the node A- side (SW3, SW4) is 10%, there is little time lag between the timing ts at which the currents i1 and i2 are detected and the timing tx at which the switches SW1 to SW4 switch between on and off. In other words, the time lag between the timing tx at which the voltage on the node A+ side switches when the duty ratio of the drive control signal Sd is equal to or greater than a predetermined threshold (e.g., 80%) and the timing ts at which the currents i1 and i2 are detected is small. As a result, the current i flowing through the coil 31 is easily affected by the switching noise of the switches SW1 and SW2, i.e., by voltage fluctuations on the node A+ side.

[0084] More specifically, in PWM period T2, the timing tx at which the voltage at node A+, which is upstream of the current path of current i, switches and the timing ts at which currents i1 and i2 are detected are close in time. Therefore, current i1 through current detection element R1, which is located on the upstream side of the current path, node A+, is more susceptible to switching noise than current i2 through current detection element R2, which is located on the downstream side of the current path, node A-.

[0085] Therefore, as described above, when the duty ratio of the drive control signal Sd is equal to or greater than a predetermined threshold, the control circuit 1A of embodiment 2 measures only the current flowing through the current detection element downstream of the current path in the drive circuit 2 (in the case of the PWM period T2 in Figure 8, the current i2 flowing through the current detection element R2 on the A-side), and uses this as the measured value of the current i flowing through the coil 31.

[0086] This makes it possible to measure the current i flowing through the coil 31 of the motor 3 with high accuracy even in a situation where switching noise is large due to the magnitude of the duty ratio of the drive control signal Sd as a PWM signal.

[0087] In the above example, when the duty ratio of the drive control signal Sd on the node A+ side (SW1, SW2) is 90% and the duty ratio of the drive control signal Sd on the node A- side (SW3, SW4) is 10%, only the current i2 flowing through the current detection element R2 on the A- side, which is downstream of the current, is measured and used as the measurement value of the current i flowing through the coil 31, but this is not limited to this. For example, if the duty ratio of the drive control signal Sd on the node A- side (SW3, SW4) is 90% and the duty ratio of the drive control signal Sd on the node A+ side (SW1, SW2) is 10%, only the current i1 flowing through the current detection element R1 on the A+ side, which is downstream of the current, is measured and used as the measurement value of the current i flowing through coil 31.

[0088] That is, when the duty ratio of either the voltage on the node A+ side (drive control signal Sd for switches SW1 and SW2) or the voltage on the node A- side (drive control signal Sd for switches SW3 and SW4) is equal to or greater than a predetermined threshold (e.g., 80%), the control circuit 1A detects the current flowing in the current detection element on the other side (the node side whose duty ratio is less than the predetermined threshold) and calculates the measured value of the current i flowing in the coil 31.

[0089] <<Extension of Embodiment>> The invention made by the present inventors has been specifically described above based on an embodiment, but it goes without saying that the invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0090] For example, in the above embodiment, the motor 3 is a stepping motor, but this is not limited to this. The motor 3 may be, for example, a three-phase brushless DC motor having coils of U phase, V phase, and W phase, and the type of motor is not particularly limited.

[0091] Furthermore, the method for detecting the rotation angle and rotation speed of the motor is not limited to the above-described method. For example, if the motor unit 100 is configured without a rotation position detector 4 (sensorless system), the control circuit 1 may calculate the rotation angle θ and rotation speed ω of the motor by a known calculation related to the sensorless system. [Explanation of symbols]

[0092] 1, 1A... control circuit, 2... drive circuit, 3... motor, 4... rotational position detector (encoder), 10, 10A... motor drive control device, 11... drive control section, 12, 12A... current acquisition section, 13... rotational speed acquisition section, 14... position acquisition section, 15... drive command acquisition section, 16... position control section, 17... speed control section, 18... current control section, 19... drive control signal generation section, 21, 22... switching leg, 31... coil, 100... motor unit , 121...first current detection unit, 122...second current detection unit, 123, 123A...current value calculation unit, 124...duty ratio determination unit, SW1 to SW4...switches, R1, R2...current detection elements, Se...rotational position detection signal, Si...current detection signal, Sc...drive command signal, Sd...drive control signal (PWM signal), i...current flowing in coil 31, i1...current flowing in current detection element R1, i2...current flowing in current detection element R2.

Claims

1. a control circuit that generates a drive control signal for driving a coil of the motor based on a measurement value of a current flowing through the coil; a drive circuit that drives the coil based on the drive control signal generated by the control circuit, the drive circuit includes a first switch and a second switch connected in series, a third switch and a fourth switch connected in series, a first current detection element connected in series with the first switch and the second switch, and a second current detection element connected in series with the third switch and the fourth switch; the coil is connected between a first node to which the first switch and the second switch are commonly connected and a second node to which the third switch and the fourth switch are commonly connected; the control circuit measures the current flowing through the coil based on an average value of the current flowing through the first current detection element and the current flowing through the second current detection element; The drive control signal is a PWM signal, When the duty ratio of the PWM signal is smaller than a predetermined threshold, the control circuit measures the current flowing in the coil based on an average value of the current flowing in the first current detection element and the current flowing in the second current detection element, and when the duty ratio of the PWM signal is equal to or greater than the predetermined threshold, measures the current flowing in the coil based on the current flowing in one of the first current detection element and the second current detection element, which is provided on a current path after the current flows in the coil. Motor drive control device.

2. 2. The motor drive control device according to claim 1, When the duty ratio of the PWM signal is equal to or greater than the predetermined threshold, the current flowing through the coil is measured based on the current flowing through one of the first and second current detection elements, which is downstream of the current path in the drive circuit. Motor drive control device.

3. 3. The motor drive control device according to claim 1, The control circuit detects at least one of the current flowing through the first current detection element and the current flowing through the second current detection element at a predetermined timing in one cycle of the drive control signal. Motor drive control device.

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